Sugar-sweetened beverage consumption has increased greatly among children since the 1960s, in parallel with the pediatric obesity epidemic, and now accounts for >10%of energy intake among adolescents. Several lines of evidence suggest that sugar-sweetened beverage consumption has a remarkably strong effect on body weight in overweight children: 1) mechanistic studies indicate that humans do not compensate fully for the energy in sugar-containing liquids;2) cross-sectional studies find consistent associations betweeen consumption of sugar-sweetened beverages and total energy intake or body weight; 3) a longitudinal study found that risk of becoming obese in middle school students increased 60% for every additional serving per day of sugar-sweetened beverage;4) short-term interventional studies found that adults who substitute non-caloric for sugar-sweetened beverages loss weight;5) a school-based study reported lower incidence of obesity among children counseled to reduce all soft drinks;6) our pilot data indicate that the effect of decreasing sugar-sweetened beverage consumption on body weight in school children is highly correlated with baseline body weight, revealing a unique sensitivity among children above the 85th percentile for BMI. For this long-term, large-scale multi-site study, we have partnered with 5 high schools in the greater Boston area and a major regional supermarket. Participants will be 240 high school students who drink at least 1 serving of sugar-sweetened beverage per day and who have a BMI >85th percentile. Participants will be randomly assigned to intervention or control groups. The intervention, of 1-year duration, will be performed on the home environment (including delivery of non-caloric beverages as done in our pilot study) and at the school (including education and behavioral modification aimed at reducing sugar-sweetened beverage consumption), focusing both on participants and the parents. Our primary endpoint will be change in BMI z-score at 2 years (1 year after conclusion of the intervention). The study has been designed to demonstrate definitively whether or not an intervention focused exclusively on beverage consumption is efficacious in the prevention and treatment of obesity in children. These results should have immediate public health application, and aid in the design of future, comprehensive obesity prevention interventions.